Inhibition of 45Ca movements by lowered temperature or lanthanum in rat brain slices

Different components of 45Ca movements in rat cortex, striatum and hypothalamus slices were delineated by conditions and ions which selectively alter Ca2+ uptake, binding or extrusion. Equilibration of 45Ca was qualitatively similar in all three tissues and was attained within 30--60 min. The 45Ca tissue-medium ratios obtained in 1.5 mM Ca2+ solutions were increased 15--30% in 0.1 mM Ca2+ solutions and doubled in 0-Ca solutions. Efflux of 45Ca from slices can be described in terms of two components. Lowering the temperature to 0 degree C increased 45Ca uptake into the slower washout component and markedly decreased 45Ca efflux. Exposure to 1.5 mM La3+ decreased both 45Ca uptake and efflux. The inhibitory effects of 0 degree C and La3+ on 45Ca efflux were additive. Uptake of 45Ca in slices incubated in 1.5 mM Sr 2+-substituted (0-Ca) solutions was more similar to that in 0-Ca solutions than in 1.5 mM Ca2+ solutions. Thus, Ca2+ distribution is qualitatively similar in slices from different rat brain areas, loss of 45Ca is an energy dependent process which is at least partially coupled to Ca2+ uptake, decreased temperature inhibits Ca2+ extrusion, La3+ impedes uptake and subsequent binding of Ca2+, and Sr2+ does not prevent the major portion of 45Ca uptake at cellular binding sites. Use of 0 degree C and La3+ to inhibit discrete components of Ca2+ fluxes in rat brain area slices provides a basis for investigation of the mechanisms by which other agents can alter Ca2+ distribution in the central nervous system.